The present invention relates to fibre reinforced composite materials suitable for sports applications, aerospace applications and general industrial applications, and to a thermosetting resin composition and a prepreg for obtaining these composite materials. In more detail, it relates to a prepreg and carbon fibre reinforced composite materials, which can be suitably used, for example, as various frames, pipes and shafts, curved discs for airplanes, ships, motor vehicles, bicycles, etc. and also for industrial machines such as pumps and bush cutters, furthermore as various sports/leisure articles such as golf club shafts, fishing rods, ski poles, badminton racket shafts, tent poles and other tubes, and ski boards, snow boards, and golf club heads, moreover as civil engineering and architectural materials and repairing and reinforcing materials thereof, etc.
On account, in particular, of their outstanding mechanical strength properties, fibre reinforced composite materials using a prepreg as an intermediate base material comprising reinforcing fibre and a matrix resin are widely employed in sports applications, aerospace applications and general industrial applications. Especially in sports applications, golf club shafts, fishing rods, rackets of tennis, badminton, etc., sticks of hockey, etc. are important applications.
In these applications, carbon fibre, aramid fibre and glass fibre are chiefly employed as the reinforcing fibre. Of these, carbon fibre is outstanding in its specific strength and specific modulus and it is particularly important in that high performance composite materials can be obtained.
Both thermoplastic resins and thermosetting resins are used as the matrix resin, but thermosetting resins are most often employed because of their excellent impregnation of the reinforcing fibre.
As thermosetting resins, epoxy resins, resins with a plurality of polymerizable unsaturated bonds in the molecule (vinyl ester resins, unsaturated polyester resins and the like), phenolic resins and cyanate resins are chiefly used. Especially in sports applications, carbon fibre is mainly used as the reinforcing fibre, and an epoxy resin, as the matrix resin.
For producing fibre reinforced composite materials, various methods are adopted. However, the method of using a prepreg as a sheet-like intermediate base material obtained by impregnating reinforcing fibre with a matrix resin is widely used. In this method, a plurality of sheets of a prepreg are laminated and heated, to obtain a formed article.
Fibre reinforced composite materials for sports such as golf club shafts and fishing rods are especially required to be lighter in weight, but the materials lighter in weight must be higher in strength.
As an approach to meet this requirement, efforts have been made to improve the reinforcing fibre, particularly carbon fibre, and many achievements have been made. However, precise analysis of breaking phenomena of golf club shafts and fishing rods, particularly those lighter in weight has revealed that it is not sufficient to only enhance the strength of carbon fibre.
Golf club shafts and fishing rods are usually produced by winding a unidirectional prepreg in several layers in different directions for lamination. When such composite materials are broken, the breaking mode depends on the material constitution and the external force acting manner (bending, torsion, crushing, etc.), but the breaking mode of either 0xc2x0 (direction parallel to the reinforcing fibre) compression or 90xc2x0 (direction perpendicular to the reinforcing fibre) tension at any layer is often a dominant factor. Next dominant is the breaking mode by shearing. Among them, the 0xc2x0 compressive strength depends on the compressive strength of the reinforcing fibre, the adhesion between the reinforcing fibre and the matrix resin, and the elastic modulus of the matrix resin, and can be enhanced by increasing their values.
On the other hand, the 90xc2x0 tensile strength depends on the tensile strength of the matrix resin. The tensile strength of the matrix resin tends to be higher when the elastic modulus and tensile elongation of the matrix resin are higher. However, the elastic modulus and tensile elongation of the matrix resin are in such a mutually sacrificial relation that one of them can be enhanced at the sacrifice of the other, and it has been difficult to enhance both simultaneously. Furthermore, even if the tensile strength of the matrix resin is enhanced, since the adhesion between the reinforcing fibre and the matrix resin is insufficient, rupture occurs at the boundary region between the reinforcing fibre and the matrix resin, making it difficult to let the obtained fibre reinforced composite material have sufficient mechanical strength properties.
So, to let the obtained fibre reinforced composite material have steadily high mechanical strength properties without relying on the material constitution and the external force acting manner, it is essential to enhance the tensile strength and elastic modulus of the matrix resin and also to enhance the adhesion between the reinforcing fibre and the matrix resin.
Furthermore, it is known that enhancing the adhesion between the reinforcing fibre and the matrix resin has an effect of enhancing the shear strength of the composite material, and that in addition to the effect of enhancing these static strength properties, it has an effect of enhancing dynamic strength properties such as impact resistance.
So, to let the obtained fibre reinforced composite material have steadily high mechanical strength properties without relying on the material constitution and the external force acting manner, it is essential to enhance the tensile strength and elastic modulus of the matrix resin and also to enhance the adhesion between the reinforcing fibre and the matrix resin.
A known means for improving the adhesion between the reinforcing fibre and the matrix resin is surface treatment of the reinforcing fibre, for example the silane coupling agent treatment of glass fibre and the electrolytic oxidation of carbon fibre. In particular, in the case of carbon fibre, when adhesion is improved by electrolytic oxidation, this is at the expense of the fibre strength so that there are limits thereto, and while there has been a strong demand for alternative means for improving the adhesion, no effective means has hitherto be found.
Simply applying any treatment to the reinforcing fibre has a limit in improving the adhesion between the reinforcing fibre and the matrix resin. It can be considered to improve the adhesion by modifying the matrix resin. At present, there is a finding that adding a certain thermoplastic resin to an epoxy resin composition generally used as the matrix resin is effective, but the effect achieved is still insufficient.
Fibre reinforced composite materials are formed variously for respective applications. When the form is a tube, strength properties such as tensile strength, compressive strength, bending strength and torsional strength are considered as important properties, and efforts are made to enhance these strength properties.
However, in recent years, for light weight members restricted in the degree of design freedom such as golf club shafts, the impact strength and radial compressive strength of a tube attract attention in addition to said strength properties, but since it is difficult to identify the factors for enhancing these properties inspite of various tests performed, it is difficult to improve those properties for making products with sufficient strength properties.
The objective of the present invention is to offer a prepreg capable of providing carbon fibre reinforced composite materials excellent in various properties, and to offer carbon fibre reinforced composite materials with such excellent properties.
In more detail, the objective of the present invention is to solve the conventional problems as described above, by offering a prepreg and carbon fibre reinforced composite materials with excellent properties, for example, a prepreg and carbon fibre reinforced composite materials capable of providing golf club shafts excellent in bending strength and torsional strength, and yet excellent in the radial compressive strength and impact strength of cylindrically formed articles.
In order to realise these objectives, the prepreg of the present invention comprises the following compositional components.
A prepreg, formed by impregnating carbon fibre with an epoxy resin composition containing the following components (A) and (B):
(A) an epoxy resin
(B) a curing agent
characterized in that the matrix resin content Wr (wt %) of the prepreg, the 0xc2x0 tensile modulus E (GPa) of the carbon fibre and the inplane shear strength S (MPa) of the carbon fibre reinforced composite material obtained by heating and curing the prepreg satisfy the following formulae (i) and (ii).
Sxe2x89xa7xe2x88x92205xc3x97LOG(E)+610xe2x80x83xe2x80x83(i)
15xe2x89xa6Wrxe2x89xa640xe2x80x83xe2x80x83(ii)
The carbon fibre reinforced composite materials of the present invention are carbon fibre reinforced composite materials comprising cured aforesaid thermosetting resin composition and reinforcing fibre.